 Introduction
• What it is?
• Why Cross-Layer ?
• Optimization Goals
 Pros and Cons
 What are the Challenges
 What are the research problems
 Future tasks
 Conclusions
• A significant recent advances that demonstrate that wireless
resources such as (time, frequency, power, link data rates, and enduser data rates), across multiple layers can be incorporated into a
unified optimization framework.
What it is?
 To create infrastructure and algorithms to enable more optimal
performance of the wireless system, by adopting an integrated,
multi-layer approach.
 The design and optimization process will combine
• Innovations at physical layers
• Control and scheduling at MAC layer
• Efficient routing and admission control at network layer
• Dynamics and flow control at transport layer
• Specific requirements at application layers.
Optimization Goals
– Lengthen system lifetime
– Enable large scale networks
• Low cost
• High efficiency
• Improve power efficiency
• Prevent system deconstruction
– Support node versatility
• Multiple functionality
• Multiple applications
Why Cross-Layer?
• Possibility
– Optimization goals can be pursued in multiple layers
– layered optimizations assume cross-layer cooperation
– Some applications do not need all layers
• Multi-hop Local Positioning System (MLPS)
• Necessity
– Optimizing single layer is not enough
– Optimizations may be conflict with each other
• One-for-all consolidate design for feasible applications
Why Cross-Layer? (Contd.)
• Heterogeneity
– Intra connection vs. Inter connection
• Scalability
– Correctness verification
• Reusability
– Code reuse
– Module reuse
• Service Consistency – Stable, consistent service quality is a basic
requirement. If the consumer’s experience is inconsistent, he or she
will be less likely to continue subscribing to the service.
• Connection Reliability – Reliable connections are extremely
important to build consumer confidence in 3G services. A dropped
connection during a wireless data session is more disruptive than a
dropped voice call.
• Consistent Multimedia Streaming – Streaming video and audio
are the key services that differentiate 3G from 2G/2.5G networks. In
a wireless WAN, RF variations can lead to long, initial buffering
times and additional interruptions during viewing.
 While applying Congestion control algorithms in a wireless
environment, network efficiency problems occur:
• Redundant data is transmitted – Congestion control algorithms
induce retransmissions resulting in redundant data transmissions
and multiple acknowledgements of data already received.
• Less bandwidth is utilized – When congestion control kicks in
(break down/smash), the rate at which packets are sent is reduced,
thereby failing to exploit valuable bandwidth.
• Sessions are terminated – When the protocol inaccurately
determines that a connection has timed out, the session will
terminate. Due to this response, some applications, like ecommerce, may be impossible to use.
What are Challenges?
• Improved Coverage – Transport optimization can increase effective
cell coverage so that in areas where a user previously could not
download a Web page due to poor signal quality, a user now can do
so quickly. Carriers are able to deliver consistent service quality over
a larger area without having to increase base station density.
• More Capacity, Higher Returns – Wireless networks have limited
capacity due to limited spectrum. With a cross-layer optimization
approach, mobile service providers increase network and spectrum
utilization, freeing up usable bandwidth and available capacity.
• Increased Throughput (document sending) and Improved
Multimedia Performance – Cross-layer optimization can increase
application throughput up to nine times, improving the user
experience and resulting in faster browsing, shorter buffering times
for multimedia, and fewer interruptions in all cell areas.
Research Problems
Cross-Layer Design With Fairness
Constant-Overhead/Low-Overhead Implementation:
Tightness of Throughput-Loss Bounds
Nonconcave Utility Functions
The Congestion-Control Problem
The Scheduling Problems
• Propagation Delays and Connection-Level Stability Analysis
• Traffic Arriving at all Nodes on the Route Instantaneously
• Complexity Issues and Distributed Algorithms for General Physical
Interference Models
Future Tasks
• Do some theoretical study on the system limitations
– System Throughput & Network Scale
– Node Synchronization and Positioning accuracy
– Channel allocation and Mode decision
– Identify and justify feasible application models
• Implement the applications
– Complete the protocol stacks
– Tune the protocols and functional modules
– Optimize the applications
– Developing the research platform
While the progress in this area has been substantial over the last
few years, there are still several open problems, especially in the
area of multihop wireless networks, where scalability becomes a
critical issue.
• While the application can adapt to a rate-delay-performance tradeoff
curve offered by the network and underlying links, by making the
lower layer protocols aware of the tradeoffs inherent to the
application adaptation, that tradeoff curve might be adjusted to
improve end-to-end performance without using up more resources in
the network.
• In other words, if the application is aware of the lower layer protocol
tradeoffs and these protocols aware of the application tradeoffs,
these tradeoffs curves can be merged to operate at the best point
relative to end-to-end performance.
Conclusions (contd.)
• While implementing this philosophy, in spite of open research
problem, it holds significant promise for the performance of ad hoc
wireless networks
• In today’s wireless world, consumers are demanding secure, highquality wireless data services to access their most important
business, news and entertainment content while they are mobile.
• By employing a cross-layer optimization solution that works
transparently at the transport and application layer, the Web,
streaming multimedia, e-mail and other applications perform at a
level users expect.
Thank you